Because noise-canceling headphones can eliminate external ambient noise, consequentially users can enjoy music without volume up the music or have a nice sleep on airplanes, trains or buses. Therefore, noise-canceling headphones are becoming more and more popular.
However, the conventional noise-canceling headphone is powered by batteries for a noise-canceling circuit therein. Thus, the conventional noise-canceling headphone may have relatively-large size and increasing weight, which may cause an inconvenience for users.